This relationship between macrophage surface components and endocytic activity is under investigation. Previously we analyzed the binding and internalization of macroglobulin protease complexes (alpha M.P) mediated by high affintity rabbit alveolar macrophage surface receptors. Data suggested that surface receptors for alpha M.P complexes were reutilized. Thus the same complement of surface receptors could repeatedly mediate ligand internalization. Current efforts are directed towards (1) obtaining further evidence as to whether receptors for alpha M.P complexes are reutilized (2) examination of the topological distribution of alpha M.P-surface receptors and (3) an examination of receptor activity in subcellular membrane fractions. The results of these studies will yield information on the dynamics of functional macrophage membrane components.